DEFINITION:- “An animal cell is a type of eukaryotic cell that lacks a cell wall and has
a true, membrane-bound nucleus along with other cellular organelles.”
ANIMAL CELL OVERVIEW:-
• Animals, fungi, and protists all have eukaryotic cells, Eukaryotic cells are
distinguished by the presence of a nucleus and other membrane-bound
• Animal cells, do not have a cell wall. Instead, multicellular animals have
a skeleton which provides support for their tissues and organs. Likewise,
animal cells also lack the chloroplasts.
• Animal cells are considered heterotrophic, this means animal cells must
obtain nutrients from other sources, by eating plant cells or other animal
• All eukaryotic cells, animal cells have mitochondria. These organelles are
used to create ATP from various sources of energy including carbohydrates,
fats, and proteins.
• Besides mitochondria, many other organelles are found within animal cells
which help them carry out the many functions required for life (Nucleus ,
ribosomes, Endoplasmic Reticulum, Golgi Apparatus, lysosomes,
• Most animal cells are diploid, meaning that their chromosomes exist in
homologous pairs. In sexual reproduction, the cellular process
of meiosis is first necessary so that haploid daughter cells, or gametes, can
be produced. Two haploid cells then fuse to form a diploid zygote, which
develops into a new organism as its cells divide and multiply.
• Plant cells are the basic unit of life in organisms of the kingdom Plantae. They
are eukaryotic cells, which have a true nucleus along with specialized
structures called organelles that carry out different functions. Plant cells have
special organelles called chloroplasts which create sugars via photosynthesis.
• Plant cells are differentiated from the cells of other organisms by their cell
walls, chloroplasts, and central vacuole. The chloroplasts within plant cells
can undergo photosynthesis, to produce glucose. In doing so, the cells use
carbon dioxide and they release oxygen.
• Plants are considered autotrophic because they produce their own food and
do not have to consume any other organisms. Specifically, plant cells
are photoautotrophic because they use light energy from the sun to produce
• The other components of a plant cell, the cell wall and central vacuole, work
together to give the cell rigidity. The plant cell will store water in the
central vacuole, which expands the vacuole into the sides of the cell. The cell
wall then pushes against the walls of other cells, creating a force known
as turgor pressure.
• Turgor pressure between cells allows plants to grow tall and reach more
• The nucleus contains a cell’s deoxyribonucleic acid
(DNA), its genetic material. DNA contains
instructions for making proteins, which controls all
of the body’s activities.
• In the nucleus, DNA is tightly winded around
histones, which are proteins, to form structures
called chromosomes. The nucleus regulates which
genes are expressed in the cell, which controls the
cell’s activity and functioning and will be different
depending on the type of cell.
• DNA is located in the nucleolus region of the
nucleus, where ribosomes are made. The nucleus is
surrounded by a nuclear envelope (also
called nuclear membrane), which separates it from
the rest of the cell.
• The nucleus also regulates the growth and division
of the cell. When the cell is preparing to divide
during mitosis, the chromosomes in the nucleus
duplicate and separate, and two daughter cells are
• Organelles called centrosomes help organize DNA
during cell division. Cells usually have one nucleus
• All living cells have a plasma membrane that encloses their contents. In prokaryotes, the membrane is
the inner layer of protection surrounded by a rigid cell wall. Eukaryotic animal cells have only the
membrane to contain and protect their contents. These membranes also regulate the passage of
molecules in and out of the cells.
• The plasma membrane separates the interior of the cell from the extracellular environment. Its
predominant components are proteins and lipids, the fundamental structure of the membrane is
the phospholipid bilayer, plasma membranes consist of approximately 50% lipid and 50% protein by
weight, with the carbohydrate portions of glycolipids and glycoproteins constituting 5 to 10% of the
• The plasma membrane, also called the cell membrane, In bacterial and plant cells, a cell wall is attached
to the plasma membrane on its outside surface.
• The Golgi apparatus, also called the Golgi complex or Golgi body, is also made up of cisternae, but
the cisternae are not interconnected like those of the ER. The Golgi apparatus receives proteins
from the ER and folds, sorts, and packages these proteins into vesicles.
• It resides at the intersection of the secretory, lysosomal, and endocytic pathways. It is of particular
importance in processing proteins for secretion, containing a set of glycosylation enzymes that
attach various sugar monomers to proteins as the proteins move through the apparatus.
• It was identified in 1897 by the Italian scientist Camillo Golgi and was named after him in 1898
Synthesis of golgi bodies
• The process of cellular respiration occurs in
the mitochondria. During this process, sugars and
fats are broken down and energy is released in the
form of adenosine triphosphate (ATP). ATP powers
all cellular processes, and mitochondria produce a
cell’s ATP, so mitochondria are commonly known as
“the powerhouse of the cell”.
• It has a double membrane, the inner part being
folded inwards to form layers (cristae).
• Mitochondria are commonly between 0.75 and
3 μm² in area but vary considerably in size and
• In addition to supplying cellular energy,
mitochondria are involved in other tasks, such
as signaling, cellular differentiation, and cell death,
as well as maintaining control of the cell cycle
and cell growth.
• The first observations of intracellular structures
that probably represented mitochondria were
published in the 1840s. Richard Altmann, in 1890,
established them as cell organelles and called
them "bioblasts".The term "mitochondria" was
coined by Carl Benda in 1898.
• The endoplasmic reticulum (ER) is a network of membranous sacs called cisternae that
branches off from the outer nuclear membrane. It modifies and transports proteins that are
made by ribosomes. There are two kinds of endoplasmic reticulum, smooth and rough. Rough
ER has ribosomes attached. Smooth ER does not have ribosomes attached and has functions
in making lipids and steroid hormones and removing toxic substances.
• Ribosomes are where proteins are synthesized. They are found within all cells, including animal
cells. In the nucleus, a sequence of DNA that codes for a specific protein is copied onto a
complementary messenger RNA (mRNA) chain. The mRNA chain travels to the ribosome via
transfer RNA (tRNA), and its sequence is used to determine the correct placement of amino
acids in a chain that makes up the protein. In animal cells, ribosomes can be found freely in a
cell’s cytoplasm, or attached to membranes of the endoplasmic reticulum.
• FUNCTION: Ribosomes are a cell structure that makes protein. Protein is needed for
many cell functions such as repairing damage or directing chemical processes. Ribosomes can be
found floating within the cytoplasm or attached to the endoplasmic reticulum
• Peroxisome is a membrane-
bound organelle (formerly known as
a microbody), found in the cytoplasm of virtually
all eukaryotic cells. Peroxisomes are oxidative
organelles. Frequently, molecular oxygen serves
as a co-substrate, from which hydrogen
peroxide (H2O2) is then formed. Peroxisomes
owe their name to hydrogen peroxide generating
and scavenging activities. They perform key
roles in lipid metabolism and the conversion
of reactive oxygen species.
The main function of these microbodies is
digestion. Lysosomes break down cellular
waste products and debris from outside the
cell into simple compounds, which are
transferred to the cytoplasm as new cell-
•Microfilaments are solid rods made of
globular proteins called actin.
•Microfilaments, also called actin
filaments, are protein filaments in
the cytoplasm of eukaryotic cells that
form part of the cytoskeleton.
• Microfilaments are usually about
7 nm in diameter and made up of two
strands of actin.
•Microfilament functions include
cytokinesis, amoeboid movement, cell
motility, changes in cell shape,
endocytosis and exocytosis, cell
contractility, and mechanical stability
•Microtubules are major components of
the cytoskeleton. They are found in all
eukaryotic cells, and they are involved
in mitosis, cell motility, intracellular
transport, and maintenance of cell
•Microtubules are composed of alpha-
and beta-tubulin subunits assembled
into linear protofilaments.
•Microtubules can grow as long as 50
micrometres and are highly dynamic.
The outer diameter of a microtubule is
between 23 and 27 nm while the inner
diameter is between 11 and 15 nm
CILIA AND FLAGELLA:- For single-celled eukaryotes, cilia and flagella are essential for
the locomotion of individual organisms. In multicellular organisms, cilia function to
move fluid or materials past an immobile cell as well as moving a cell or group of cells.
ENDOSOMES AND ENDOCYTOSIS:- Endosomes are membrane-bound vesicles,
formed via a complex family of processes collectively known as endocytosis, and found
in the cytoplasm of virtually every animal cell. The basic mechanism of endocytosis is
the reverse of what occurs during exocytosis or cellular secretion. It involves the
invagination (folding inward) of a cell's plasma membrane to surround macromolecules
or other matter diffusing through the extracellular fluid.
•Centrioles are cylindrical, self-replicating organelles composed mainly of a protein called tubulin
made up of microtubules and Centrioles are found in most eukaryotic cells. They appear to help in
organizing cell division.
•A bound pair of centrioles, surrounded by a shapeless mass of dense material, called the
pericentriolar material, makes up a structure called a centrosome
•Intermediate filaments are one of three types of cytoskeletal elements. The other two
are thin filaments (actin) and microtubules. Frequently the three components work
together to enhance both structural integrity, cell shape, and cell and organelle
motility. Intermediate filaments are stable, durable.
•Ranging in size from 8 to 12 nanometers
Vesicles are small spheres of a lipid bilayer,
which also makes up the cell’s outer
membrane. They are used for transporting
molecules throughout the cell from one
organelle to another and are also involved in
metabolism. Specialized vesicles called
lysosomes contain enzymes that digest large
molecules like carbohydrates, lipids, and
proteins into smaller ones so that they can be
used by the cell.
The cytosol is the liquid contained within cells. Cytosol and all the organelles within it,
except for the nucleus, are collectively referred to as a cell’s cytoplasm. This solution is
mostly made of water, but also contains ions like potassium, proteins, and small
molecules. The pH is generally neutral, around 7.
The cytoskeleton is a network of filaments and tubules found throughout the cytoplasm
of the cell. It has many functions: it gives the cell shape, provides strength, stabilizes
tissues, anchors organelles within the cell, and has a role in cell signaling. There are
three types of cytoskeletal filaments: microfilaments, microtubules, and intermediate
filaments. Microfilaments are the smallest, while microtubules are the biggest.
ANIMAL CELLS FUNCTION
• Cells carry out all the processes of the body including producing and storing energy,
making proteins, replicating the DNA, and transportation of molecules through the
body. Cells are highly specialized to carry out specific tasks. For example, the heart
has cardiac muscle cells that beat in unison. Digestive tract cells have cilia, which are
finger-like projections that increase surface area for the absorption of nutrients during
digestion. Each cell type has the organelles suited to its particular task.
• There are over 200 different types of cells in the human body. Red blood cells contain
hemoglobin, the molecule that carries oxygen, and they have no nuclei; this is a
specialization that allows each red blood cell to carry as much oxygen within it as
• Multiple cells form tissues. These groups of cells carry out a specific function. In turn,
groups of similar tissues form the body’s organs, such as the brain, lungs, and
heart. Organs work together in organ systems, like the nervous system, digestive
system, and circulatory system. Organ systems vary depending on the species.
• For example, insects have open circulatory systems, where blood is pumped directly into
body cavities and surrounds their tissues. Vertebrates such as fish, mammals, and
birds, on the other hand, have closed circulatory systems. Their blood is enclosed within
blood vessels where it travels to target tissues. In this way, all animal have evolved
specific uses for each of the cells in their bodies.
• Chloroplasts are found only in plant
and algae cells. These organelles carry out the process
of photosynthesis, where the photosynthetic
pigment chlorophyll captures the energy from sunlight,
converts it, and stores it in the energy-storage
molecules ATP and NADP while freeing oxygen from
water in plant and algal cells. They then use the ATP
and NADPH to make organic molecules from carbon
dioxide in a process known as the Calvin cycle.
• Chloroplasts carry out a number of other functions,
including fatty acid synthesis, much amino
acid synthesis, and the immune response in plants.
• They are oval-shaped and have two membranes: an
outer membrane, which forms the external surface of
the chloroplast, and an inner membrane that lies just
beneath. Between the outer and inner membrane is a
thin intermembrane space about 10-20 nanometers
wide. Within the other membrane, there is another
space called the stroma, which is where chloroplasts
• Chloroplasts themselves contain many flattened disks
called thylakoids, and these have a high concentration
of chlorophyll and carotenoids, which capture light
energy. The molecule chlorophyll also gives plants their
green color. Thylakoids are stacked on top of one
another in vascular plants in stacks called grana.
The cell wall is a tough layer found on the outside of the plant cell that gives it strength and also
maintains high turgidity. In plants, the cell wall contains mainly cellulose, along with other molecules
like hemicellulose, pectin, and lignins. The composition of the plant cell wall differentiates it from the
cell walls of other organisms.
For example, fungi cell walls contain chitin, and bacterial cell walls contain peptidoglycan, and these
substances are not found in plants. The main difference between plant and animal cells is that plant
cells have a cell wall while animal cells do not. Plant cells have a primary cell wall, which is a flexible
layer formed on the outside of a growing plant cell, and a secondary cell wall, a tough, thick layer
formed inside the primary plant cell wall when the cell is mature.
• Plant cells are unique in that they have a large central vacuole. A vacuole is a small sphere
of plasma membrane within the cell that can contain fluid, ions, and other molecules. Vacuoles are
basically large vesicles. They can be found in the cells of many different organisms, but plant cells
characteristically have a large vacuole that can take up anywhere from 30-80 percent of the cell.
• The central vacuole of a plant cell helps maintain its turgor pressure, which is the pressure of the
contents of the cell pushing against the cell wall. A plant thrives best when its cells have high
turgidity, and this occurs when the central vacuole is full of water. If turgor pressure in the plants
decreases, the plants begin to wilt. Plant cells fare best in hypotonic solutions, where there is more
water in the environment than in the cell; under these conditions, water rushes into the cell
by osmosis , and turgidity is high.
• Animal cells, on the other hand, can lyse if too much water rushes in; they fare better
in isotonic solutions, where the concentration of solutes in the cell and in the environment is equal
and net movement of water in and out of the cell is the same.
PLANT CELL TYPES
There are five types of plant cells, each with different
Parenchyma cells are the majority of cells in a plant.
They are found in leaves and carry out
photosynthesis and cellular respiration, along with
other metabolic processes. They also store
substances like starches and proteins and have a
role in plant wound repair.
Collenchyma cells provide support to growing parts
of a plant. They are elongated, have thick cell walls,
and can grow and change shape as a plant grows.
Sclerenchyma cells are hard cells that are the main
supporting cells in the areas of a plant that have
ceased growing. Sclerenchyma cells are dead and
have very thick cell walls.
Xylem cells transport mostly water and a few
nutrients throughout a plant, from the roots to the
stem and leaves.
Phloem cells transport nutrients made during
photosynthesis to all parts of a plant. They transport
sap, which is a watery solution high in sugars.
PLANT CELL FUNCTIONS
Plant cells are the basic building block of plant life, and they carry out all of the functions
necessary for survival. Photosynthesis, the making of food from light energy, carbon dioxide, and
water, occurs in the chloroplasts of the cell. The energy molecule adenosine triphosphate (ATP) is
produced through cellular respiration in the mitochondria.